Add cuDNN support for F.dropout
Add cuDNN support for F.dropout

wkentaro/chainer,keisuke-umezawa/chainer,niboshi/chainer,keisuke-umezawa/chainer,chainer/chainer,okuta/chainer,jnishi/chainer,hvy/chainer,keisuke-umezawa/chainer,okuta/chainer,keisuke-umezawa/chainer,hvy/chainer,ktnyt/chainer,chainer/chainer,jnishi/chainer,jnishi/chainer,ktnyt/chainer,wkentaro/chainer,niboshi/chainer,jnishi/chainer,okuta/chainer,wkentaro/chainer,chainer/chainer,ronekko/chainer,rezoo/chainer,hvy/chainer,hvy/chainer,niboshi/chainer,pfnet/chainer,ktnyt/chainer,niboshi/chainer,wkentaro/chainer,ktnyt/chainer,okuta/chainer,tkerola/chainer,chainer/chainer